Cheiroballistra
= Introduction = This reconstruction is based on analysis of the available English editions of the cheiroballistra (Marsden 1971: 206-233; Wilkins 1995: 10-33). Ideas from earlier scholars, especially Iriarte (2000; 2003), are utilized where they seem to make sense. Additionally I've used the manuscript diagrams available in Schneider's (1906) and Wescher's (1867) editions. Analysis of the archaeological finds is mostly based on the numerous publications of Baatz. In this article and reconstruction I've made a few underlying assumptions and followed a few key principles: * Pseudo-Heron's (P.H.) cheiroballistra text assumed to be more or less complete. No parts are assumed missing, unless it's certain that the reconstruction can't work without them * Archaeological finds are given preference to text in case of ambiguities. They are, however, only used to make design decisions where the text fails. Dimensions from archaeological finds are not used, even if they seem similar to those in the text. * The goal has been to make the reconstruction fit the text, not vice versa. This principle is followed as far as reasonably possible. For a good example of this principle, see discussion below about the tenons of the rungs in the little ladder. * I do not try to hide problems in the source material or in my own theories. Therefore I've tried to make it clear what we really know and what is subjective. My goal is to make (constructive) critique as easy as possible, not to protect myself from critique by not mentioning the issues I've encountered. The cheiroballistra text is a description of interrelated ballista components. Although the assembly instructions are very incomplete, the fact that parts must fit together helps a lot in making the reconstruction correct. If an incorrect change is made to dimensions of some component, it is likely that problems arise elsewhere. There are two possibilities to coping with this. The first option is what some scholars unfortunately seem to do: hang on to their assumptions and force the sources to fit them. For discussion of this issue see Iriarte's JRMES article (2000: 56-57). The second option is to question one's underlying assumptions and think "outside the box", trying to find the most logical explanation to the problem. I have tried to follow the second option according to my best ability. I've also followed Occam's razor by choosing the simplest explanation from among competing explanations that all explain the data equally well. One big problem with the work of many previous scholars is that they have ignored the limitations of the metalworking techniques and tools used by the Greeks and the Romans. To arrive at a realistic reconstruction, these need to be taken into account. Again, there's a good example of this in the little ladder section. = Main controversies = Outswinger or inswinger Archaeological finds strongly suggest that the cheiroballistra was an inswinger so I've reconstructed it as such. This issue has already been discussed in detail here. Winched or not winched? The cheiroballistra was almost certainly a personal weapon and as such did not have a winch. The reasons for this are discussed in detail on this page. = Conventions = All measurements are in Greek dactyls (1,93cm). The way dimensions are marked in the CAD drawings requires explanation: * Dimensions which are clearly stated in the cheiroballistra text are marked in green. Even these dimensions may be suspect as it is not always clear what P.H. means by width, thickness, length and breadth. That said, the vast majority of these dimensions can't really be questioned. * Dimensions which roughly know are marked in orange. These are the ones given in the text as "about x dactyls". This applies mostly to the slider width. * Dimensions which are derivable from other dimensions are marked in magenta. These dimensions are not stated in the text, but can be calculated from dimensions of other parts. This applies especially to thickness of the field frame bars, which are referred to throughout the text. * Dimensions which are entirely subjective and not given in text are marked in red. These dimensions are the ones which have allowed scholars to reconstruct the cheiroballistra as a winched weapon without amending the text too heavily. In the few cases where the clearly stated or roughly known dimensions have been amended, the following notation has been used: * X d (Y d) * X d (Y d) Where X is the amended measurement and Y the original measurement stated by P.H. = Cheiroballistra parts = Case The case is the lower part of the cheiroballistra stock with a female dovetail groove running down it's length. The upper part of the stock, slider, has the male dovetail which allows it to slide on top of the case. Although the description of the case (e.g. Marsden 1971: 213) is relatively clear compared to most other sections in Heron's cheiroballistra, it can still be interpreted in a number of ways. The part describing the location of the projecting block (ΚΘ) is corrupt in all manuscripts and does not make sense as is. A simple solution to this corruption was suggested first by Prou's (1877: 120-121) and later Iriarte's (2000: 48). Both simply substituted ΑΘ with ΛΘ and the text makes perfect sense. While this theory sounds most plausible to me, other explanations have been suggested by Marsden (1971: 218), Wilkins (1995: 11-12), Schneider (1906: 149) and Baatz (1974: 70). The actual purpose of the projecting block has confused pretty much every researcher, as Iriarte (2000: 48) points out. I have interpreted it simply as a support for the little ladder holding the field frames. This is the simplest solution to keep the little ladder, the field frames and the little arch from moving backwards when the weapon is cocked. Of course, some additional ironwork is needed, but much less than without support from the projecting block. As Wilkins (1995: 12) notes, removing wood along ΛΘ and ΑΚ as suggested by Heron (e.g. Marsden 1971: 213) seems silly. It seems clear that Heron is not thinking like a carpenter, who would have simply glued or nailed a piece of wood to bottom of the board ΑΒ and be done with it - as did I. Full CAD drawing of the case below: Slider The slider has a male dovetail corresponding to the female dovetail in the case. Although a relatively simple component, it's exact form is still not clear. There are two competing interpretations for the slider's cross-section: * Most scholars (e.g. Marsden 1971: 218, Wilkins 1995: 11) have reconstructed the slider from two pieces forming a "T" shape. The lower part of this composite construction was the male dovetail to which the upper part was attached. The upper part simply rests on top of the case. * Iriarte (2000: 52) suggests that the slider was made from one piece. These differing interpretations stem from the fact that Heron did not state how wide the female dovetail should be; he only gives it's depth (1d) and length (46d). He also says that the slider should be "about" 2,5d wide and 1,25d high. The "T" proponents take 2,5d to mean the width of the upper (non-dovetail) part of the slider, whereas Iriarte (2000: 52) suggests that the male dovetail itself - being the only part of the slider - was about 2,5d wide. I've personally followed Iriarte's interpretation as it is simpler and requires one to make fewer questionable assumptions. The "about" (see Iriarte 2000: 52) in slider width requires some discussion. If the slider was 2,5d wide, then only 0,5d (or ~1cm) of wood would be left on both sides of the slider. This is not much, but might be enough for durable operation. Nevertheless, I've made the slider slightly narrower (2d). Crescent-shaped piece The crescent-shaped piece (ΗΒ) has a rectangular hole in it's middle and it's attached to the end of the case. Apparently a rectangular tenon was pushed through this hole and into the stock to keep it firm. None of it's dimensions are given by P.H. The crescent-shaped piece is used to push the slider backwards with stomach pressure. This interpretation is almost universally accepted by all scholars, with the notable exception of Alan Wilkins (1995; 2000, 2003). There is no need to find any other explanations unless one is predetermined to interpret the cheiroballistra as a winched weapon like Wilkins did. Little ladder The description of the little ladder (ΛΜΝΞΟΠΡΣ) is relatively clear (e.g. Marsden 1971: 215-216; Wilkins 1995: 26-29). Only the part describing the tenons (ΛB, ΝΓ, ΟΔ, ΡΕ) is very vague and further evidence has to be sought for from archaeological finds. It is highly likely that the tenon parts of the little ladder were similar to those in the Orsova kamarion (Baatz 1978: 11). The lower surface of the boards ΛΜΝΞ and ΟΠΡΣ was probably curved, as Wilkins (1995: 29) notes. The thickness of the boards themselves is not given. Several scholars have arrived at widely different translations or interpretations of the same section of the text: Marsden (1971: 215), referring to the beams (ΛΜΝΞ and ΟΠΡΣ): The thickness each is to be 0,5d, and the length? of each of the tenons ... is to be 2d Wilkins (1995: 28): Let the thickness of each of the Tenons ... be 1/2 dactyl. Iriarte (2000: 57): The thickness of each one of the tenons ... must be 2 d. Marsden's 0,5d for the thickness of the board is completely arbitrary addition. Again, the lack of thickness figure allows anyone to make the little ladder just as strong as is required. The material for the boards is usually assumed to be iron. In case the boards were made of iron, 0,5 d (~1cm) as suggested by Marsden is way too strong (and heavy) for a gastraphetes-style weapon. A more realistic figure would be 0,17 dactyls (~0,35cm). Although the cheiroballistra text is apparently describing boards made of iron, hardwood could be used instead: 0,75d thick boards should be strong enough. In any case, the boards had rectangular holes at Τ and Υ and round holes at Φ, Χ, Ψ and Ω. Each board had three holes which were the same distance (=equidistant) from each other. Although not clearly stated, the distance between the ends of the boards and the outermost holes should almost certainly be the same. Both Marsden (1971: 225) and Wilkins (1995: 29) apparently misinterpreted this part of the text, placing the round holes at the same distance from the center on both boards. This meant that without an extra pair of holes the rungs would rotate. The correct way is to treat both boards separately and not just copy the locations for holes from one beam to the other. As the boards are of different length, the holes do not coincide, which prevents the rungs from rotating as suggested by Iriarte (2000: 58). In fact, I had reached the same conclusion before reading Iriarte's article. Similarly, the hole in the middle is rectangular to prevent the cross-piece from rotating. The crosspiece (ΤΥ) and rungs (ΦΧ and ΨΩ) are placed between the two boards (ΛΜΝΞ and ΟΠΡΣ) as spacers. All of the are told to be 3d long (not counting the tenons) and 2,5d wide. The thickness is not given, which leaves open many interpretations. Most well-known scholars have made the crosspiece and rungs from thick iron plate. If we assume that the crosspiece and rungs were made from iron, there were only two practical ways to make them with tools and techniques of that time: * Forging the crosspieces, rungs and their tenons from the same piece of iron. This requires forging a flat iron plate and then chiseling away excess material from around the tenons. After this the tenons of the rungs have to be forged round. This last step is entirely unnecessary, as the holes in the boards had to be punched anyways and punching round and rectangular holes is as easy. Regardless, this whole process would have been relatively fast. * Welding the tenons to the crosspieces and rungs. This technique does not waste material, but involves lots of welding of small pieces of iron. As each tenon and it's corresponding crosspiece or rung had to be heated to welding heat together, the risk of melting the crosspiece or the rungs was high. The process would also have been pretty slow and would have consumed lots of charcoal. For these reasons this technique seems unlikely. Some modern reconstruction are made by boring holes through the rungs and inserting tenons through them (e.g. Wilkins 1995: 28). This was not feasible in antiquity, where the only realistic method of making holes to thick pieces of iron was punching. While punching through the beams - even very thick ones - is trivial, punching a hole accurately through a relatively narrow but 3d (~6cm) thick piece of steel is not an option. Other modern reconstructors don't clearly state how their crosspieces and rungs are made (e.g. Iriarte 2000: 58; Marsden 1971: 225). And alternative explanation is that instead of iron cross-piece and rungs wooden spacers were used. They could have been the same height as the boards. According to Marsden (1971: 217) P.H. states that the cross-piece was riveted. Wilkins (1995: 28) uses the term "to pin" instead of "to rivet". In any case, there's no talk of riveting (or pinning) the round tenons of the rungs. This would imply that they were left loose and in fact, there's no need to attach them securely: the ends of the boards are securely held together by the metal hoops of the field frames and the middle by the rectangular rivet going through the cross-piece. This allows both the cross-piece and the rungs to be made of wood without any difficulty, their only metal component being the rectangular iron rivet going through the crosspiece and beams. The wooden spacers would be trivial to make, much lighter than their iron counterparts and would even support the little ladder better because of their greater height. The rungs would have had round holes to which round wooden (or iron) tenons were inserted. Little arch The little arch (ΑΒΓΔΕΖΗ) is the upper support strut for the field frames. Field frames Bars Field frames are spring-frames used to house the spring cord. Wescher's (1867) edition of the cheiroballistra does not unfortunately include pictures of these bars. Fortunately Schneider's edition (1906: 154) does. However, best illustrations are in Wilkins' edition (1995: 18). In addition, there are several archaeological finds of field-frames. There are two field frames in each cheiroballistra, each consisting of one curved bar (ΔΒ and ΗΘ) and one straight bar (ΓΑ and ΕΖ). To the end of these bars two rings are attached at ΚΛ, ΜΝ, ΞΟ and ΠΡ. In codex M's diagram (see Wilkins 1995: 18) the Ζ is clearly in the wrong place - it should be next to Π. This does not affect the interpretation in any way, though. Below is a diagram of the field-frame bars: The characteristic curve in the middle of outer bars is formed by bending the thicker side of the bar. This method was used on some of the archaeologically attested field-frames, namely in Orsova and Lyon artefacts. This makes sense, as it does not make the curved bar too weak to withstand the pressure of the torsion springs. In Gornea field-frames the curved bar was bent along it's thinner side. However, the curved part of the bar was significantly widened, almost certainly to prevent the pressure of the spring cord from bending it. The curve in Gornea field-frames also seemed to be more modest than that in Orsova and Lyon field-frames. The Sala field-frame was cast from broze and it follows the Orsova / Lyon style. Rings Pi-brackets Washers Triggering mechanism The triggering mechanism in cheiroballistra text is very vaguely described. Fortunately the manuscript diagrams (see Wescher 1867 and Schneider 1906) clarify the text a lot. Regardless, dimensions of the components are lacking; only the length of the incision in the claw is given. This reconstruction of the trigger is based on Iriarte's (2000) work. Wilkins reconstruction, though commendable, is based on the idea that cheiroballistra had a winch (1995: 14-17). Fork Similarly to the claw, all authors agree upon the general appearance of the fork (ΕΖΗΘ). Wilkins (1995: 14) calls this component double bracket and tenon. The part ΕΖ is a double bracket and ΗΘ a rectangular tenon. The double bracket is bored at ΤΥ to receive an axle. The same axle is pushed through the hole bored at Φ in the claw. The fork is sunk to the slider from it's rectangular tenon end and riveted (from below). Note that the letters in manuscript diagrams don't exactly match what we'd expect looking at the text. Claw The claw (ΚΛΜ) is well-known from older artillery pieces, so there is little disagreement on it's general form (see Marsden 1971: 219-220; Wilkins 1995: 17; Iriarte 2000: 52-53). The claw has an incision of 1 dactyl long and has a horizontal, round hole at Φ. This hole is used for the claw axle which also goes through holes in the fork. Trigger Similarly to the claw and fork the general form of the trigger (ΝΞ) is well know and agreed upon. Wilkins (1995: 14) has translated this component as the snake. A round hole is punched or bored to the trigger (from top) at Ν. A corresponding hole is bored to the slider (ΓΔ) at Π. An axle is then inserted through both holes. This allows the trigger to rotate around it's axle on top of the slider. Handle The interpretation of the handle (ΑΒΓΔ) depends on whether one reconstructs a winched weapon or not. The general form is handle is surely the same as that shown below: In the text it's stated clearly that there's a round hole at Δ, at the bottom of the handle. A corresponding hole is bored to the slider (ΓΔ) at ΜΝ. The handle and slider are then attached together with a pin/axle. Also, a rectangular hole is pierced to the slider at Ξ. The location of this second, rectangular hole is only marked into one of the manuscript diagrams - it is located just behind the round hole (ΜΝ) (see Wescher 1867: 127-128). Iriarte (2000: 52-53) interpreted the rectangular hole as a lengthwise, rectangular incision extending forward from the end of the slider. In Iriarte's reconstruction the handle rotated freely up and down, which was necessary to lock and unlock it to it's anchor (a strong nail) at the end of the draw and after release. Wilkins (1995: 16-17) placed the handle horizontally and used it as attachment point for the winch. He made the rectangular hole perpendicular to the stock, which allowed him to make the handle stronger. This suited his winched cheiroballistra scheme better. Pi bracket The Π (pi) bracket (ΟΠΡΣ) is one of the most controversial parts of the triggering mechanism. Marsden (1971: 221-222) thought it to be a rivet-plate to which other triggering mechanism parts were attached to. Gudea & Baatz (1974: 62), followed by Wilkins (1995: 16) and Iriarte (2000: 53-54) interpreted it as handgrip for pushing the slider forward. Wilkins (1995: 16) placed the pitarion in front of the fork, whereas Iriarte (2000: 53-54) placed it behind it. Either approach seems to work in practice and has little effect on the functionality of the machine - if the handgrip interpretation is correct. Arms Add description of the arms... Wilkins (1995; 2003) lengthened the metal hooks of the arms arbitrarily because he had issues with too short draw length. This in turn was caused by placing of the little ladder too close to the front of the case. From engineering point of view lengthening the metal hooks was also very unwise: it places too much stress on the end of the metal hook, which would have otherwise been supported by the very rigid wooden arm. Lengthening the hook requires it to be made much thicker and thus heavier. As the arm is only a method by which energy is transmitted to the bowstring and to the bolt, it should be as light as possible. The heavier the ballista arms are, the more energy they waste, especially if their forward momentum is stopped by the heels of the arms and not the bowstring. A taut bowstring would at least transfer some of the wasted energy into the bolt. = Assembling the components = Foreword Correctly reconstructing the cheiroballistra involves assembling the components so that they work perfectly together. If some of the individual parts are misinterpreted, problems almost certainly arise when assembling the components. Marsden (1971) and Wilkins (1995) encountered a number of these problems because they had arbitrarily changed various dimensions of the cheiroballistra. I've used the relationship and interaction of the components as a guide: if the components don't seem to fit together, there more likely an issue with the interpretation rather than the sources themself. Alignment of the field-frame bars The distance between the field-frame bars is given as 3,5 d. We also know that the ring to which these bars are attached has external diameter 4 d and internal diameter of 2d. This is about all we know for certain. However, it is possible to align the field-frame bars so that these conditions are met and any assumptions made intuitive enough to be omitted by P.H. - either intentionally or by mistake. This rules out some of the more imaginative solutions suggested by some scholars. As Iriarte (2000: 54-55) points out, all of the field-frame rings of manuscript diagrams (see Iriarte 2000: 54; Schneider 1907: 154-155; Wilkins 1995: 18) are pointed ellipses, not circles. Similarly, all of the archaeological field-frame rings are more or less pointed ellipses, Orsova field-frame ring being a good example of this. Therefore my cheiroballistra field-frame rings to some extent share this same feature. I also make a few other assumptions: * Tenons of the little ladder beams are roughly identical in dimensions and form. * The inner sides of the field-frame bars and extremities of the little ladder beams (not their tenons) are in contact. * The center of the ring, washer and cord bundle is halfway between the ladder beams. Given these assumptions, there is really only one way to align the field-frame bars correctly, if they're placed offset (left). If the bars are placed radially (right), another reconstruction is possible: As can be seen above right radially placed field-frame bars require an asymmetrical ring; otherwise the curved bar will inevitably be farther from the ring's edge than the straight one. The beauty of the alignment above left - when coupled with the assumptions stated above - is that it requires no trickery or long chains of dependent arguments to support it. For these reasons I've chosen to align my field-frame bars as shown above on the left. The above placement of bars and rings will naturally make the cheiroballistra an inswinger. It is not possible to reconstruct any archaeological field-frame as an outswinger, and the close relation between those and the cheiroballistra has been acknowledged even by the outswinger proponents. This issue is discussed in more detail in here. Little ladder, field-frames and arms The little ladder, field-frame bars and field-frame's pi-brackets need to fit together perfectly. The description of each of these components is relatively clear, except for the tenons of the little ladder beams. Unfortunately P.H. does not tell us how these components should be assembled - therefore archaeological finds are crucial in solving this problem. Below is a diagram displaying how these parts fit together. Little arch and washers are omitted for clarity: As mentioned above, the projecting block under the case has been interpreted as a supporting block for the little ladder, which is very intuitive. Without this support block the T-clamps have to be exceedingly strong to prevent the little ladder from moving backwards. Wilkins (1995: 11) interpreted the block as an attachment point for the base whereas Marsden (1971: plates 7-8) ultimately ignored it. Both placed the little ladder close to the forward end of the case where it was not supported by the projecting block. This soon lead both into issues with draw length: even when the arms were drawn to the maximum, the slider was not entirely pulled back. The only way to fix this issue was to lengthen the arms, which allowed longer draw length (Marsden 1971: 226; Wilkins 1995: 33). As the length of the "cones" or wooden portions was known, only the metal hooks could be lengthened without contradicting the text. As explained above, lengthening the hooks beyond the cones is a bad idea. Also, as can be seen from the above diagram there's no reason to lengthen the arms to obtain the correct draw length with an inswinger. Interestingly same draw length can be obtained with an outswinger, too (Iriarte 2000: 65). Another interesting thing visible in the above diagram is the huge arc (~170 degress) the arms can rotate. Take a look here to see how this is achieved. Without this amount of arm movement it would not be possible to draw the slider back fully in an inswinging cheiroballistra. The placing of the field-frame bars is also worth mentioning: they are placed right where the little ladder beams end and their tenons would start. As can be seen, the little ladder beams can be made to fit exactly between the field frames. This is interesting, because it means that the Pi-brackets of the field-frame bars would then have to be placed inside the field-frames, not outside like in the archaeological field-frames found so far. This would still leave a 2-3mm space between the the Pi-brackets and the torsion bundle before the arm is inserted. However, the little arch can't be made to fit the field-frames this easily, so it's more likely that the tenons of little ladder beams were bent and were pushed through Pi-brackets located on the outside surface of the field-frame bars as in archaeological field-frames. = Author and contributors = Author: Samuli Seppänen Category:backup